Yes, by default I believe it runs tests sequentially.
JUnit 4.6 introduced an experimental ParallelRunner
to run tests in parallel - I don't know of its current status. I would expect parallelism to remain an "opt-in" feature by default though. (Judging by other answers, it looks like this is now here to stay but in a slightly different form - and still opt-in.)
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…